Variable frequency drive temperature determination

ABSTRACT

Temperature value determination of at least one variable frequency drive component is provided. In one form, a method includes providing a variable frequency drive that includes a first component in thermal communication with a second component in thermal communication with a switching device. A temperature value of the second component is determined using a temperature value of the first component, a power loss characteristic of the drive, and a first characteristic of heat transfer between the first and second components. The method further includes sensing a temperature value of the second component and determining a temperature value for the switching device using the power loss characteristic, a second characteristic of heat transfer between the second component and the switching device, and the greater of the sensed and determined temperature values of the second component. Further embodiments, forms, features, and aspects shall become apparent from the description and drawings.

BACKGROUND

The present application relates to the determination of temperaturevalues of one or more components of a variable frequency drive, and moreparticularly but not exclusively, to the determination of a temperaturevalue of a switching device of the variable frequency drive.

As the use of variable frequency drives to control electric motorsbecomes more commonplace, further advances in the design and operationof the same are desired. For example, the temperature of the internaljunction of a switching device of a variable frequency drive can be alimiting factor to its operation. Indeed, if the maximum temperaturerating of the internal junction of the switching device is exceeded,then damage and/or failure of the variable frequency drive may result.In contrast, the life and reliability of the variable frequency drivemay be enhanced by not exceeding the maximum temperature rating of theinternal junction of the switching device. Readily knowing thetemperature of the internal junction of the switching device can bebeneficial for avoidance of exceeding its maximum temperature rating;however, the internal junction temperature of a switching device is noteasily measured. In view of the foregoing, there is a demand for furtherimprovements in this area of technology.

SUMMARY

Temperature value determination of at least one component of a variablefrequency drive is provided. More particularly, in one embodiment, amethod includes providing a variable frequency drive that includes afirst component in thermal communication with a second component inthermal communication with a switching device. A temperature value ofthe second component is determined using a temperature value of thefirst component, a power loss characteristic of the drive, and a firstcharacteristic of heat transfer between the first and second components.The method further includes sensing a temperature value of the secondcomponent and determining a temperature value for the switching deviceusing the power loss characteristic, a second characteristic of heattransfer between the second component and the switching device, and thegreater of the sensed and determined temperature values of the secondcomponent.

In another embodiment, a method includes providing a variable frequencydrive including a first component in thermal communication with a secondcomponent in thermal communication with a switching device; determininga temperature value of the second component using a temperature value ofthe first component, a power loss characteristic of the drive, and afirst characteristic of heat transfer between the first component andthe second component; sensing a temperature value of the secondcomponent; and determining a temperature value for the switching deviceusing the power loss characteristic, a second characteristic of heattransfer between the second component and the switching device, and thegreater of the sensed temperature value of the second component and thedetermined temperature value of the second component.

In still another embodiment, a system includes inverter circuitryincluding one or more transistors in thermal communication with asubstrate, a heat sink in thermal communication with the invertercircuitry, and a controller. The controller is configured to determine atemperature of the heat sink, determine a temperature of the substrateas the greater of a sensed temperature value of the substrate and acalculated temperature value of the substrate based upon the determinedtemperature of the heat sink, and determine an internal temperature ofthe one or more transistors based upon the determined temperature of thesubstrate and a thermal impedance between the substrate and the one ormore transistors.

In yet another embodiment, a method includes determining a firsttemperature value of a first component of a system including a variablefrequency drive using a temperature value of a second component of thesystem in thermal communication with the first component, a power losscharacteristic of the drive, and a thermal impedance between the firstand second components. The method also includes sensing a temperaturevalue of the first component; determining a second temperature value ofthe first component using the sensed temperature of the first componentand a thermal time constant of the first component; and determining atemperature value for a third component of the system in thermalcommunication with the first component using the greater of the firstdetermined temperature value of the first component and the seconddetermined temperature value of the first component, the power losscharacteristic of the drive, and a thermal impedance between the firstand third components.

Other aspects include unique methods, systems, devices, kits,assemblies, equipment, and/or apparatus related to estimating ordetermining a temperature value of one or more components of a variablefrequency drive.

Further aspects, embodiments, forms, features, benefits, objects, andadvantages shall become apparent from the detailed description andfigures provided herewith.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of an exemplary system including avariable frequency drive.

FIG. 2 is a schematic illustration of the variable frequency drive ofthe system of FIG. 1.

FIG. 3 is a photographic image of a portion of the variable frequencydrive of FIG. 2.

FIG. 4 is a schematic illustration of an equivalent circuit thermalmodel.

FIG. 5 is a schematic illustration of a technique for implementing themodel of FIG. 4.

FIG. 6 is a schematic illustration of an alternative embodimentequivalent circuit thermal model.

FIG. 7 is a schematic illustration of a technique for implementing themodel of FIG. 6.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

For purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

In one aspect, an approach for determining or estimating a temperaturevalue of at least one component of a variable frequency drive isprovided. In one form, a method includes providing a variable frequencydrive that includes a first component in thermal communication with asecond component in thermal communication with a switching device. Atemperature value of the second component is determined using atemperature value of the first component, a power loss characteristic ofthe drive, and a first characteristic of heat transfer between the firstand second components. The method further includes sensing a temperaturevalue of the second component and determining a temperature value forthe switching device using the power loss characteristic, a secondcharacteristic of heat transfer between the second component and theswitching device, and the greater of the sensed and determinedtemperature values of the second component. Further embodiments, forms,features, and aspects shall become apparent from the description anddrawings.

The temperature value determination or estimation of at least onecomponent of a variable frequency drive disclosed herein may beperformed or conducted in connection with a variable frequency drivebeing used in one of a variety of different applications. By way ofnon-limiting example, one application including a variable frequencydrive where the temperature value of at least one of its components maybe determined or estimated is chiller system 100 illustrated in FIG. 1.Chiller system 100 includes a refrigerant loop that includes acompressor 110, a condenser 120, and an evaporator 130. Refrigerantflows through system 100 in a closed loop from compressor 110 tocondenser 120 to evaporator 130 and back to compressor 110. Variousembodiments may also include additional refrigerant loop elementsincluding, for example, valves for controlling refrigerant flow,refrigerant filters, economizers, oil separators and/or coolingcomponents and flow paths for various system components.

Compressor 110 is driven by a drive unit 150 including an electric motor170 which is driven by a variable frequency drive 155. In one form,variable frequency drive 155 is configured to output a three-phase PWMdrive signal, and motor 170 is a surface magnet permanent magnet motor.Use of other types and configurations of variable frequency drives andelectric motors such as interior magnet permanent magnet motors,reluctance motors, or inductance motors are also contemplated. It shallbe appreciated that the principles and techniques disclosed herein maybe applied to a broad variety of drive and permanent magnet motorconfigurations.

Condenser 120 is configured to transfer heat from compressed refrigerantreceived from compressor 110. In one form, condenser 120 is a watercooled condenser which receives cooling water at an inlet 121, transfersheat from the refrigerant to the cooling water, and outputs coolingwater at an output 122. It is also contemplated that other types ofcondensers may be utilized, for example, air cooled condensers orevaporative condensers. It shall further be appreciated that referencesherein to water include water solutions comprising additionalconstituents unless otherwise limited.

Evaporator 130 is configured to receive refrigerant from condenser 120,expand the received refrigerant to decrease its temperature and transferheat from a cooled medium to the refrigerant. In one form, evaporator130 is configured as a water chiller which receives water provided to aninlet 131, transfers heat from the water to the refrigerant, and outputschilled water at an outlet 132. It is contemplated that a number ofparticular types of evaporators and chiller systems may be utilized,including dry expansion evaporators, flooded type evaporators, bare tubeevaporators, plate surface evaporators, and finned evaporators amongothers.

Chiller system 100 further includes a controller 160 which outputscontrol signals to variable frequency drive 155 to control operation ofmotor 170 and compressor 110. Controller 160 also receives informationabout the operation of drive unit 150 including, but not limited to,information relating to motor current, motor terminal voltage, and/orother operational characteristics of motor 170 and variable frequencydrive 155. It shall be appreciated that the controls, control routines,and control modules described herein may be implemented using hardware,software, firmware and various combinations thereof and may utilizeexecutable instructions stored in a non-transitory computer readablemedium or multiple non-transitory computer readable media. It shallfurther be understood that controller 160 may be provided in variousforms and may include a number of hardware and software modules andcomponents such as those disclosed herein.

Turning now to FIG. 2, one non-limiting arrangement of variablefrequency drive 155 is schematically illustrated. Variable frequencydrive 155 includes a switching device 180 positioned on and in thermalcommunication with a thermally conductive base or substrate 190.Switching device 180 includes one or more internal switching junctionsand in one non-limiting embodiment is in the form of one or moreinsulated gate bipolar transistors (IGBT's). In another form, switchingdevice 180 is a power MOSFET. With reference to the photographic imageof FIG. 3 for example, variable frequency drive 155 includes a pluralityof IGBT's 182. Base 190 may be formed from a variety of differentthermally conductive materials or combinations of materials. Forexample, in one particular but non-limiting form, base 190 is formedfrom copper or an alloy thereof. A thermal pad 200 is positioned betweenbase 190 and a heat sink 210, although forms in which thermal pad 200 isomitted and base 190 is positioned directly on heat sink 210 are alsocontemplated. It should further be understood that forms in which one ormore additional components are positioned between switching device 180and base 190 and/or between base 190 and heat sink 210 are possible.

Heat sink 210 is formed of a thermally conductive material and is inthermal communication with base 190 and a cooling medium 220. In thisarrangement, heat sink 210 is configured to absorb heat created byswitching device 180 during operation of variable frequency drive 155and transfer the heat to cooling medium 220. Cooling medium 220 may bein any form suitable for absorbing and moving heat away from heat sink210, examples of which include air, water, glycol or a refrigerant, justto provide a few possibilities. In one particular but non-limiting form,cooling medium 220 is refrigerant of the refrigerant loop that includescompressor 110, condenser 120, and evaporator 130, and heat istransferred away from heat sink 210 by the refrigerant. In another form,cooling medium 220 could be part of a separate heat transfer system thatincludes a closed loop of cooling medium 220 and a heat exchangerconfigured to release heat from cooling medium 220 to ambientenvironment or another cooling medium, although other variations arepossible.

Variable frequency drive 155 also includes a number of sensorspositioned at different locations and configured to measure temperaturesand provide sensed temperature values to controller 160. Moreparticularly, variable frequency drive 155 includes sensor 192configured to measure temperature of base 190 and provide a sensedtemperature value of base 190 to controller 160, sensor 212 configuredto measure temperature of heat sink 210 and provide a sensed temperaturevalue of heat sink 210 to controller 160, and sensor 222 configured tomeasure temperature of cooling medium 220 and provide a sensedtemperature value of cooling medium 220 to controller 160. In theillustrated embodiment, variable frequency drive 155 includes a singlesensor at each separate location. In other non-illustrated formshowever, variable frequency drive 155 includes a plurality of sensors ateach location such that a plurality of sensed temperature values areprovided to controller 160 for each of base 190, heat sink 210 andcooling medium 220. Forms in which variable frequency drive 155 does notinclude a sensor at one or more of these locations, or includes sensorsat locations in addition to or in lieu of these locations, are alsopossible.

With further reference to FIGS. 4 and 5, further details of onenon-limiting approach for estimating or determining a temperature valuefor an internal junction of switching device 180 and other components ofvariable frequency drive 155 will be provided. FIG. 4 is a schematicillustration of an equivalent circuit thermal model 230 which models theheat transfer characteristics between components of variable frequencydrive 155 and may be used to determine temperature values fortemperature T₂ representative of a temperature value for heat sink 210,temperature T₃ representative of a temperature value for base 190, andtemperature T₄ representative of a temperature value for the internaljunction of switching device 180. Temperature T₁ is representative of atemperature value of cooling medium 220 and may correspond to a sensedtemperature value of cooling medium 220 provided by sensor 222 or apredetermined temperature value of cooling medium 220 that may be, forexample, stored in memory of controller 160.

In model 230, resistance R₁ and capacitance C₁ represent an impedance Z₁associated with a thermal loss between heat sink 210 and cooling medium220, resistance R₂ and capacitance C₂ represent an impedance Z₂associated with a thermal loss between base 190 and heat sink 210, andresistance R₃ and capacitance C₃ represent an impedance Z₃ associatedwith a thermal loss between switching device 180 and base 190. Inaddition, P_(loss) in model 230 is representative of an estimated powerloss characteristic of variable frequency drive 155 determined bycontroller 160 based on various operating characteristics of variablefrequency drive 155.

FIG. 5 provides a schematic illustration of one non-limiting technique240 executable by controller 160 for implementing model 230 to determinetemperature values for temperatures T₂-T₄. In the illustrated form,technique 240 begins with operation 245 in which P_(loss) is multipliedby impedance Z₁. In operation 250, the result of operation 245 is addedwith temperature T₁ to provide a determined temperature value DT₁ ofheat sink 210. As indicated above, T₁ is representative of a temperaturevalue of cooling medium 220 and may correspond to a sensed temperaturevalue of cooling medium 220 provided by sensor 222 or a predeterminedtemperature value of cooling medium 220. As also indicated above, incertain forms variable frequency drive 155 may include a plurality ofsensors 222 configured to measure temperatures of cooling medium 220 andprovide a plurality of sensed temperature values of cooling medium 220to controller 160. In these forms, controller 160 may be configured toselect and use the highest of the plurality of sensed temperature valuesprovided by the plurality of sensors 222 for temperature T₁ or to use anaverage or other combination of the plurality of sensed temperaturevalues provided by the plurality of sensors 222 for temperature T₁. Inone exemplary but non-limiting example of a form in which temperature T₁represents a predetermined temperature value of cooling medium 220,temperature T₁ may correspond to a maximum temperature value thatcooling medium 220 may reach before switching device 180 exceeds a ratedthermal level.

In operation 255, determined temperature value DT₁ of heat sink 210 iscompared to a sensed temperature value ST₁ of heat sink 210 provided bysensor 212 and the greater of these two values is selected as therepresentative temperature value T₂ of heat sink 210. In forms wherevariable frequency drive 155 includes a plurality of sensors 212configured to measure temperatures of heat sink 210 and provide aplurality of sensed temperature values of heat sink 210 to controller160, controller 160 is configured to select and use the highest of theplurality of sensed temperature values provided by the plurality ofsensors 212 for temperature value ST₁. In certain forms in which T₁represents or corresponds to a predetermined temperature value ofcooling medium 220, controller 160 is configured to determine thatswitching device 180 is operating above a rated thermal level if ST₁ isgreater than DT₁. Controller 160 may also be further configured tochange one or more operating characteristics of variable frequency drive155 in order to reduce its thermal output in response to determiningthat ST₁ is greater than DT₁. In other forms where temperature T₁ isbased on a sensed temperature value of cooling medium 220 provided bysensor 222, controller 160 is configured to compare the greater of ST₁and DT₁ with a predetermined value stored in memory of controller 160for example, and if the greater of ST₁ and DT₁ exceeds the stored,predetermined value then controller 160 may determine that switchingdevice 180 is operating above a rated thermal level and change one ormore operating characteristics of variable frequency drive 155 in orderto reduce its thermal output.

In operation 260 P_(loss) is multiplied by impedance Z₂. The result ofoperation 260 is added with temperature value T₂ of heat sink 210 toprovide a determined temperature value DT₂ of base 190 in operation 265.In operation 270, determined temperature value DT₂ of base 190 iscompared to a sensed temperature value ST₂ of base 190 provided bysensor 192 and the greater of these two values is selected as therepresentative temperature value T₃ of base 190. In forms where variablefrequency drive 155 includes a plurality of sensors 192 configured tomeasure temperatures of base 190 and provide a plurality of sensedtemperature values of base 190 to controller 160, controller 160 isconfigured to select and use the highest of the plurality of sensedtemperature values provided by the plurality of sensors 192 fortemperature value ST₂. Controller 160 may also be configured todetermine that switching device 180 is operating above a rated thermallevel if ST₂ is greater than DT₂, in which case controller 160 may alsobe further configured to change one or more operating characteristics ofvariable frequency drive 155 in order to reduce its thermal output inresponse to determining that ST₂ is greater than DT₂. Alternatively,controller 160 may be configured to change one or more operatingcharacteristics of variable frequency drive 155 in order to reduce itsthermal output in response to determining that ST₂ or DT₂ is greaterthan a predetermined value stored in memory of controller 160 forexample.

P_(loss) is multiplied by impedance Z₃ in operation 275. The result ofoperation 275 is added with temperature value T₃ of base 190 to providea determined temperature value DT₃ of switching device 180, which alsocorresponds to temperature T₄ representative of a temperature value forthe internal junction of switching device 180. In one form, controller160 may be configured to change one or more operating characteristics ofvariable frequency drive 155 in order to reduce its thermal output inresponse to determining that DT₃ or T₄ is greater than a predeterminedvalue stored in memory for example that corresponds to a rated thermallevel of switching device 180. Additionally or alternatively, in theevent DT₃ or T₄ is below but approaching or otherwise below but close tothe stored, predetermined value that corresponds to the rated thermallevel of switching device 180, then controller 160 may also beconfigured to change one or more operating characteristics of variablefrequency drive 155 in order to reduce its thermal output in order toavoid exceeding the rated thermal level of switching device 180.

It should be understood that forms in which technique 240 determinestemperature values for fewer components of variable frequency drive 155are possible. For example, in one form, technique 240 may involvedetermination of temperature values T₂ and T₄ where impedance Z₃ wouldreflect the omission of the determination of temperature value T₃. Inone or more alternative forms, determination of temperature value T₂ ofheat sink 210 may be omitted from technique 240, and technique 240 maybegin by providing ST₁ as the result of operation 255. Still, it shouldbe understood that other alternatives and variations are contemplatedand possible.

Referring now to FIGS. 6 and 7, further details of another non-limitingapproach for estimating or determining a temperature value for theinternal junction of switching device 180 and other components ofvariable frequency drive 155 will be provided. FIG. 6 is a schematicillustration of an equivalent circuit thermal model 300 where likereferences refer to like features previously described. Model 300 issubstantially similar to model 230 but further accounts for delays insensing the temperature of heat sink 210 under dynamic conditions due tothe amount of thermal capacitance of heat sink 210. In model 300, R₄represents an equivalent impedance (resistive and capacitive) of thepath over which heat is nominally flowing through heat sink at a sensedlocation. C₄ represents the thermal capacity of the heat sink at asensed location. R₄ and C₄ are used to calculate a thermal time constantof heat sink 210 in technique 310 schematically illustrated in FIG. 7,where like references refer to like features previously described. Moreparticularly, in operation 315 R₄ and C₄ are used along with a sensedtemperature value ST₁ of heat sink 210 provided by sensor 212 tocalculate a thermal time constant K_(ths) of heat sink 210 according tothe following equation:

$K_{tHS} = {R_{4} \times C_{4} \times \frac{{dST}_{1}}{dt}}$In operation 320, the result of operation 315 is added with temperatureST₁ to provide a second determined temperature value DT₄ of heat sink210. In forms where variable frequency drive 155 includes a plurality ofsensors 212 configured to measure temperatures of heat sink 210 andprovide a plurality of sensed temperature values of heat sink 210 tocontroller 160, controller 160 is configured to select and use thehighest of the plurality of sensed temperature values provided by theplurality of sensors 212 for temperature value ST₁ in operations 315 and320. In operation 255, determined temperature value DT₁ of heat sink 210is compared to determined temperature value DT₄ of heat sink 210 and thegreater of these two values is selected as the representativetemperature value T₂ of heat sink 210. It should be understood thatbeyond the description provided for operations 315, 320 and 255, theremaining operations of technique 310 are executed in the same manner asdescribed above in connection with technique 240. It shall be furtherunderstood that the techniques, methods, controls, diagnostics, andlogic disclosed herein may be implemented in a variety of software,hardware, firmware, and combinations thereof.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly certain embodiments have been shown and described and that allchanges and modifications that come within the spirit of the inventionsare desired to be protected. It should be understood that while the useof words such as preferable, preferably, preferred or more preferredutilized in the description above indicate that the feature so describedmay be more desirable, it nonetheless may not be necessary andembodiments lacking the same may be contemplated as within the scope ofthe invention, the scope being defined by the claims that follow. Inreading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary.

What is claimed is:
 1. A system, comprising: inverter circuitry including one or more transistors in thermal communication with a substrate; a heat sink in thermal communication with the inverter circuitry; and a controller configured to: determine a temperature of the heat sink; determine a temperature of the substrate as the greater of a sensed temperature value of the substrate and a calculated temperature value of the substrate based upon the determined temperature of the heat sink; and determine an internal temperature of the one or more transistors based upon the determined temperature of the substrate and a thermal impedance between the substrate and the one or more transistors.
 2. The system of claim 1, further comprising a sensor configured to provide a sensed temperature value of the heat sink to the controller, wherein the controller is further configured to determine if the inverter circuitry is operating above a rated level if the sensed temperature value of the heat sink is greater than a calculated temperature value of the heat sink.
 3. The system of claim 1, wherein the one or more transistors physically contact the substrate and the substrate physically contacts the heat sink.
 4. The system of claim 1, wherein the internal temperature of the one or more transistors is a junction temperature.
 5. The system of claim 4, wherein the one or more transistors comprise one or more insulated gate bipolar transistors.
 6. The system of claim 1, further comprising a first plurality of sensors configured to provide a plurality of measured temperatures of the heat sink, and a second plurality of sensors configured to provide a plurality of measured temperatures of the substrate.
 7. The system of claim 6, wherein the controller is further configured to: determine a sensed temperature value for the heat sink based on a highest one of the plurality of measured temperatures of the heat sink; and determine the sensed temperature value for the substrate based on a highest one of the plurality of measured temperatures of the substrate.
 8. The system of claim 1, further comprising a motor electrically coupled with an output of the inverter circuitry.
 9. The system of claim 8, wherein the motor is a permanent surface magnet motor.
 10. The system of claim 1, wherein the controller is further configured to determine the temperature of the heat sink as the greater of a sensed value and a calculated value.
 11. The system of claim 10, wherein the calculated value is based upon a power lows associated with the inverter circuitry, a thermal impedance between the heat sink and a cooling medium in thermal communication with the heat sink, and one of a sensed temperature of the cooling medium and a predetermined temperature value of the cooling medium.
 12. The system of claim 10, wherein the controller is further configured to determine that the inverter circuitry is operating above a rated temperature if a highest one of a plurality of measured temperatures of the heat sink is greater than the calculated temperature value of the heat sink. 